Patent GB-1112690-A (GB)
Title: Magnetic storage device
IPC: G11C11/06
Filed: 1965-07-30
Abstract: 1,112,690. Circuits employing bi-stable magnetic elements. STANDARD TELEPHONES & CABLES Ltd. 30 July, 1965 [6 Aug., 1964], No. 32754/65. Heading H3B. A non-destructive read-out word-organized store includes a matrix of magnetic cores with one row per word and two cores per bit and a row of bi-stable circuits, one per column of pairs of cores via which information is written into and read out of the matrix. In the normal condition of the store of Fig. 1 comprising rows X1-Xn and columns Y1-Ym of cores row selecting switches SX1 to SXn are open and no premagnetizing current flows through the series-connected premagnetizing windings 1 on the cores. Since the supply voltage U is disconnected from all the bi-stable circuits FF1-FFm all the transistors are non-conductive and no current flows through any of the windings 2. For each bit of information the a and b cores are in opposite states of remanent magnetization i.e. + Br or - Br. In order to read out a word of information the appropriate word selection switch e.g. S1 is closed and switch S activated so that the premagnetizing current Jm1 is established more rapidly in the windings 1 of row 1 than the collector current of either of the transistors of all the bi-stable circuits in the row Xo. Both cores of each bit in the row are thus magnetized towards saturation in the positive direction by the magnetizing force + Hx due to current in windings 1. If the core a was initially in the negative remanent state - Br then when it is switched by the premagnetizing current a pulse is induced in winding 3 on that core which causes transistor Tr2 to become non-conductive. Thus the information stored in the bit determines which of the two transistors becomes conductive and information is read out at the output terminals E of the transistors. During the time that the row selection switch is closed the core of each pair whose winding 2 is non-conductive due to the corresponding transistor being non-conductive is held nearer to saturation than the other core which is subjected to a lesser magnetizing force since the current in winding 2 is opposite to that in winding 1. This condition of the cores is also indicative of the bit of information which was originally stored in the pair of cores. The row selection switch is then opened and the premagnetizing current Jm1 falls off more rapidly in the windings 1 than the collector current of the conducting transistors so that there is a period of time during which on one core of each pair there is no current in winding 1 but current in winding 2 resulting in this core switching to the negative remanent state i.e. the pair of cores are in their original condition. In order to write a word of information the appropriate row selection switch is closed and then opened as for reading out an input signal being applied to the corresponding input P of the transistors to reverse the condition of the bistable circuit if the information in the bit is to be changed. If a fault occurs and the supply voltage and source of premagnetizing current are disconnected during read out or write in when they should be connected then the condition of each pair of cores of the selected row wherein one of the cores of each pair is nearer saturation than the other will be retained when the circuit is reconnected so that the bistable circuits reassume the same condition they were in before the fault. In the modification of Fig. 3 (not shown) the series-connected windings 3 are connected via a transformer, amplifying switch and differentiating circuit to the base electrodes of the corresponding transistor.